Conventional clothes drying machines typically utilize an open loop control system to determine an appropriate amount of time for drying a load of clothes. The duration of drying time is determined by an operator and entered using a manual control, such as a time selector switch. The operator selects a drying time based on the desired dryness for the clothes and based on past experience with the particular machine. A longer drying time than is necessary to fully dry the clothes commonly is selected to ensure that the clothes are fully dried. Use of more time than is needed for effective drying, however, leads to a waste of energy.
To more accurately determine appropriate drying times, some known clothes drying machines include closed loop control systems. Such closed loop control systems typically include humidity sensors, temperature sensors, or both, that are used in conjunction with look up tables to estimate the weight of the load. Particularly, the length of drying time required is a function of the weight of the load and the amount of water contained in the load. By estimating the weight of the load, and knowing the temperature or humidity (or both) at selected locations in the machine, the length of drying time can be estimated.
Although such closed loop systems are useful, it would be desirable to increase the accuracy of such systems. In increasing the accuracy of such systems, it also would be desirable to minimize additional sensor cost. Increasing the accuracy of such systems without adding significant sensor costs results in savings to the consumer in the form of reduced energy consumption.